The invention relates to a booster, such as a booster that is used to transfer a detonation train between two detonating cords, for example.
A perforating gun typically is used to form tunnels in a formation to enhance the production of oil and/or gas from the formation. The tunnels are formed by detonating shaped charges of the perforating gun. In this manner, the shaped charges typically detonate in response to a shockwave, or detonation train, that propagates along a detonating cord (often called a primer cord) that contacts the shaped charges. Quite often, several perforating guns may be used to perforate the formation(s) of a wellbore in one firing sequence. As a result, the detonation train may be relayed from one perforating gun to the next, a condition that implies the detonation train is relayed between the detonating cords of the different perforating guns. One way to accomplish this is to tie the ends of the detonating cords together. However, such an arrangement may be too susceptible to failure.
Secondary explosives may be used to more effectively transfer a detonation train between two detonating cords, as the secondary explosives amplify, or boost, the detonation train due to the nature of the transfer. For example, referring to FIG. 1, a pair of detonating boosters 10 (a donor booster 10a and a receptor booster 10b) use secondary explosives to transfer a detonation train from one detonating cord 12 to another detonating cord 14. To accomplish this, the detonating booster 10 may include an explosive 20 that is located near a closed flat end 24 of a tubular shell 22. An open end 21 of the shell 22 receives an end of the detonating cord 12, 14 that ideally contacts the explosive 20. The explosive 20 in the donor booster 10a detonates in response to a detonation train from the detonating cord 12, an event that causes the end 24 of the shell 22 to break into several projectiles. If the receptor booster 10b is close enough to the donor booster 10a, the projectiles strike the end of the receptor booster 10b and detonate its explosive 20. The detonation of the explosive 20 of the receptor booster 10b, in turn, introduces a detonation train to the detonating cord 14 to complete the transfer of the detonation train. As depicted in FIG. 1, the donor 10a and receptor 10b boosters may be identical. Due to this feature, either booster 10 may be used as the donor booster, thereby making it difficult to make errors when assembling the donor and the receptor boosters 10. Not shown in FIG. 1 is a housing that typically is used to hold and position the donor 10a and receptor 10b boosters.
Due to the tolerances of other parts of the perforating gun (e.g., tolerances introduced by loading tube for shaped charges, connections, booster housing, etc.), it is difficult to have a fixed booster-to-booster air gap 40 between the ends 24 of the donor 10a and receptor 10b boosters. Because the projectiles from the donor booster 10a tend to spread apart during flight, the success of the detonation train transfer may be sensitive to the span of the air gap 40. Therefore, if the air gap 40 is too large, the projectiles may spread too far apart and not sufficiently contact the receptor booster 10b to cause detonation of its explosive 20.
Referring to 2, the success of the detonation train transfer may also be sensitive to a cord-to-booster air gap 43 that may exist between the end of the detonating cord 12, 14 and the explosive 20. This gap 43 may be attributable to, as examples, an uneven cut in the detonating cord 12, 14 or assembly error. Unfortunately, if the span of the air gap 43 is too large, the detonation train transfer may fail. For example, for the donor booster 10a, if the span is too large, a detonation train from the detonating cord 12 may not detonate the explosive 20, and for the receptor booster 10b, if the span is too large, the detonation of the explosive 20 may not initiate a detonation train on the detonating cord 14.
Thus, there is a continuing need for an arrangement that addresses one or more of the above-stated problems.
In one embodiment of the invention, a booster to relay a detonation train from a detonating cord to another booster includes an explosive and a shell. The shell has an open end to receive an end of the detonating cord and an indented closed end that is adapted to form a projectile to strike said another booster when the explosive detonates.
In another embodiment of the invention, a booster to relay a detonation train from a detonating cord to another booster includes a shell and an explosive. The shell is adapted to receive an end of the detonating cord, and the explosive is adapted to detonate in response to the detonation train. The explosive includes at least approximately fifty percent of NONA by weight, and the explosive forms at least one projectile out of the shell to strike the other booster when the explosive detonates.
Other features will become apparent from the following description, from the drawings and from the claims.